1. Field of the Invention
The present invention relates to an interferometric apparatus and an optical interferometry method for obtaining surface-shape information about an object to be inspected or phase information, such as refractive-index distribution, about a transparent object to be inspected. More specifically, the present invention relates to a moving-object measuring interferometric apparatus and an optical interferometry method for measuring a moving object that are suitable for the optical interferometric measurement of a to-be-inspected object moving with respect to the interferometric apparatus (note that the term “moving” includes the deformation of the surface of a to-be-inspected object and a change in the refractive-index distribution of the object, as well as a spatial position change and a rotational movement).
2. Description of the Related Art
A speckle interferometric apparatus for measuring the time-dependent deformation (i.e., deformation caused with the lapse of time) of an object to be inspected is generally used as the related-art apparatus for optically measuring a to-be-inspected object involving a movement. In an apparatus for measuring moire fringes, a case is also known in which a moving object to be inspected is intermittently subjected to strobe irradiation so as to obtain a moire-fringe image taken at each irradiation time.
Additionally, a proposal has been made for providing an interferometric apparatus in which a cyclically moving object to be inspected is intermittently irradiated with short pulse light synchronously with the movement cycle of the object, and reflected light obtained by each irradiation is subjected to multiple exposure, thus obtaining interference-fringe images taken at the same position of the object (see JP-A-2003-222508 ).
In recent years, a desire has increased to measure a to-be-inspected object moving along a production line according to the optical interferometry in an in-line (on-process) state. For example, in an industry to produce film materials (made of polyester resin, such as PET or PEN, polycarbonate resin, amorphous polyolefin resin, or acrylic resin) that are used for a liquid crystal display or a plasma display, there is a desire to measure the thickness non-uniformity of a film material, which depends on a manufacturing environment or a manufacturing condition, in an in-line manner at intervals of a predetermined time at a predetermined position of a production line along which the film material flows and to feed back the measurement results for controlling the manufacturing condition or the like.
For example, a method disclosed by JP-A-59-105508 is known as the related-art method for measuring the thickness non-uniformity or the like of a to-be-inspected object shaped like a highly transparent film according to the optical interferometry. However, the related-art method is based on the measurement in an off-line state, and is not based on the measurement of a to-be-inspected object moving along a production line according to the optical interferometry.
Additionally, a method disclosed by JP-A-2003-222508 mentioned above is invented for a to-be-inspected object that reciprocates cyclically, and has a problem in the fact that parts to be measured, such as those of the film material mentioned above, are moved in sequence, and hence that of JP-A-2003-222508 cannot be applied to a to-be-inspected object the same part of which has difficulty in being photographed many times.